The greatest metallurgical difficulties for aluminium refineries today are in recycling materials with a low metal content, said process being carried out in furnaces using fluxing agents, mixtures of sodium chloride (NaCl) and potassium chloride (KCl) in different proportions. The recycling of the metal is thus carried out.
The fluxing agent used, called salt slag, takes the form of large solidified cakes when it is removed from the furnace. This by-product contains the oxide and a certain amount of metal aluminium (5%-8%) occluded therein, the high price of which justifies a recovery treatment. The fluxing agent used is also recycled in the process of recycling the aluminium oxide developed from this salt slag.
The furnace for melting aluminium foam and aluminium drosses and scraps has two main objectives:                1. Recycling of salt slag, producing a fluxing agent to be reused, aluminium concentrates for re-melting and an oxide for selling.        2. A facility for cleaning the gases in which the filter dust is produced.        
The treatment of the furnace combustion gases may require the prior addition of powdered salts to neutralize the acid gases (lime or bicarbonate), activated carbon, etc. and is carried out in bag filters.
Currently, the dust is dumped given that its treatment in current salt slag recycling plants greatly alters the production process. The main interest in this case is to obtain zero dumping in this type of residues.
Different studies have been carried out to palliate this problem. The reintroduction in the furnace of the gas filtering dust was studied in the past, but it prolongs the melting and is not cost-effective due to the added dust. A more rational solution would be to mix them with the salt slag to follow the same recycling process, but the tests conducted in this sense do not recommend this with some types of dust. The filter dust is incorporated to the salt slag treatment process continuously from the transport bag (usually of the type known as the Big Bag) to a hopper, and from the latter to a vibrating feeder and a rotating auger. They are mixed on the rotating auger with the ground material coming from the salt slag, subsequently following the same treatment.
The aluminum drosses and scraps grinding filter dust were also incorporated to the process, although they are reacted differently from the salt slag grinding dust.
This way of operating by incorporating the gas filter dust from the furnaces for a certain time has given rise to a number of problems which delayed production of the facility.
The filter dust of other gas uptake facilities in the furnaces of a refinery also cause many problems for recycling them in the described manner:                They have a lower amount of soluble salts than salt slag, and the proportion of water needed is different.        They have carbonaceous compounds which hinder contact and dissolution with water.        They have much less aluminium than salt slag, and their reactivity is much lower, although not the presence of substances which must be made inert.        They have a fine particle grain size and the decanting and filtering require very special working conditions.        
Filter dust has always been difficult to handle and this is the reason they end up being dumped in a duly authorized dump site. On the other hand it has been demonstrated that a successful wet process of treating filter dust is possible. The problem is that the more toxic substances are not destroyed in this process but rather are finally incorporated to the end product, reducing its quality.
The dust resulting from the aluminium refinery gas filtering has the following approximate average characteristics:
% organic 5-25% NaCl + KCl 5-65% Al2O3 (oxides)55-65% Al (metal)1-8% SiO20-1% MgO0-1% Fe2O30-1% AlN0-1% Al2S3 + Al4C3traces% heavy metalsTraces
The organic matter are oils, fats, free carbon, tar and others.
The inventors, who are persons skilled in the art, are not aware of any system with the features described below.